1. Field of Invention
The present invention involves a novel combination of an adsorbent for sulphur compounds and a hydrogenation catalyst for use with edible oils. More particularly the invention relates to a sulphur compound-adsorbing, low-silica zeolite combined with a nickel hydrogenation catalyst in a stabilization medium, to form a combination product, which product adsorbs sulphur compounds present in edible oils while the edible oils are being hydrogenated.
2. Background Art
Supported metal catalysts are known, and their use in numerous reactions, including the hydrogenation of edible oils, has been described in the literature. These supported metal catalysts are often utilized for the hydrogenation of edible oils to increase the saturation content from a low saturation content (approximately 180 iodine value units) to a very high saturation content (as low as approximately 0.5 iodine value units). Products produced from these hydrogenated edible oil products include, for example, salad oils, margarines, shortenings, soaps, candles, and confections.
The term xe2x80x9csupported metal catalystxe2x80x9d can be defined as a catalyst, whereby an active metal precursor (nickel, palladium, copper, cobalt, etc,) is deposited on an oxide support by means of precipitation, decomposition, or impregnation. One preferred supported metal catalyst is a nickel hydrogenation catalyst. References describing nickel-supported catalysts and their uses include U.S. Pat. Nos. 5,463,096 and 5,285,346, and PCT Application Number WO 94/06557. U.S. Pat. No. 5,463,096 describes a process for the preparation of supported nickel catalysts which are used particularly for the hydrogenation of fatty acids and vegetable oils, which are contaminated with sulphur compounds at a level less than about 10 parts per million. PCT Application Number WO 94/06557 describes the preparation of supported nickel catalysts to which promotion metals (particularly zinc) are added during the precipitation stage of catalyst formation. Both of these references disclose a traditional approach to edible oil hydrogenation catalyst improvement, i.e., catalyst performance is improved by altering the structure of the catalytic precursor oxides. The support medium serves only to hold the reduced, activated metal.
Zeolite products are often used as adsorbents for sulphur compounds. The term xe2x80x9czeolitexe2x80x9d can be defined as a crystalline hydrated aluminosilicate. The basic structure of the zeolite is represented by the formula: M2/nO.Al2O3.XSiO2.YH2O, whereby M is a metal cation and X, Y, and n are numbers. Each type of zeolite has its own specific pore characteristics, which allows it to adsorb specific targeted substances. The cations present in the zeolite composition are usually Group I or Group II metals, particularly sodium or potassium. In addition to unexchanged sodium and/or potassium zeolites, the zeolite product may be ion-exchanged with other metal cations, such as zinc, copper, barium, or manganese. See, for example, U.S. Pat. Nos. 3,864,452, 4,358,297 and 5,843,300.
Zeolites or molecular sieve products are designed as physical adsorbents for a number of products, including sulphur compounds. For example, U.S. Pat. Nos. 2,882,243 and 2,882,244 disclose molecular sieves useful for the adsorbence of hydrogen sulphide and other compounds at ambient temperatures. In addition, U.S. Pat. No. 3,760,029 discloses the use of synthetic faujasites as adsorbents for dimethyldisulphide removal from normal paraffins. Further, U.S. Pat. No. 3,816,975, 4,540,842 and 4,795,545 disclose the use of a standard molecular sieve 13X as a sulphur adsorbent for the purification of liquid hydrocarbon feedstocks. See also U.S. Pat. No. 4,098,684 and the European Patent Application 781,832.
Various adsorption processes and products have been disclosed for the removal of sulphur compounds from catalytic process feed streams. In one conventional process, these adsorption products are placed upstream from the catalyst to remove the sulphur compounds from the feed stream prior to the catalyst reaction with the feed stream. Chemisorption of sulphur-containing compounds using metal or metal oxide adsorbents is the most popular method used for the removal of these sulphur compounds from these feed streams. These metal oxides may include nickel, platinum, cobalt or copper in zerovalent form or zinc, manganese, cadmium, or copper oxides, either alone or secured to a support structure. For example, U.S. Pat. No. 4,634,515 discloses a sulphur trap adsorbent for sulphur-sensitive, reforming catalyst protection, wherein the catalyst comprises nickel on a support. At least 50 percent of the nickel is in a reduced zerovalent state. U.S. Pat. No. 4,204,947 discloses copper metal, copper oxide, or copper chromite secured on an inorganic porous carrier as an adsorbent for the removal of mercaptans from hydrocarbon oils. U.S. Pat. No. 4,179,361 describes an adsorbent for mineral oil purification which comprises cobalt oxide on a porous alumina. U.S. Pat. No. 4,225,417 discloses the use of manganese or manganese oxide on a support for sulphur scavenging and catalytic reforming catalyst protection.
In an effort to decrease adsorbent costs, the use of multistaged purification has been suggested. For example, U.S. Pat. No. 4,446,005 discloses a guard bed for reforming catalysts which comprises two components: nickel metal on an activated alumina, or aluminosilicate and copper, zinc, or chromium oxide on a porous support. U.S. Pat. No. 5,322,615 discloses nickel or platinum on alumina as a first step adsorbent, and potassium on alumina as a second step adsorbent. U.S. Pat. No. 5,106,484 teaches a three stage purification using a NaY synthetic zeolite, nickel on an activated alumina, and manganese oxide as adsorbents for sulphur compounds.
Particular types of zeolite with transition metal oxides have also been disclosed for the adsorption of sulphur compounds in U.S. Pat. Nos. 4,188,285; 5,057,473; 5,146,036; 5,807,475, and 5,843,300.
The hydrogenation process for edible oils is usually accomplished using a slurry phase reactor. During that process, a specified amount of edible oil is placed within a stirred/heated vessel with a measured amount of catalyst. Under elevated temperature and pressure, the catalyst hydrogenates the edible oil. Problems frequently arise during this process when the edible oil contains sulphur compounds. These sulphur compounds poison the hydrogenation catalysts used during the slurry phase. Nickel catalysts, which are useful for the hydrogenation reaction, are especially sensitive to sulphur poisoning on their active surfaces. Poisoning of these nickel catalysts results in longer then desired hydrogenation times, undesired side reaction products and, in some instances, poor quality of the finished product.
Accordingly, it is an aspect of this invention to provide an edible oil hydrogenation catalyst which is protected from catalytic poisoning by an adsorbent xe2x80x9cin situxe2x80x9d with the catalyst.
It is a further aspect of the invention to provide a nickel-based hydrogenation catalyst that is combined with a zinc-exchanged form of a low-silica faujasite adsorbent either alone or preferably with a stabilization medium for the adsorption of sulphur compounds present in a feed stream.
It is a still further aspect of the invention to provide a combination sulphur adsorbent and hydrogenation catalyst, whereby the adsorption rate of the adsorbent is equal to or higher than the adsorption rate of the hydrogenation catalyst.
It is a further aspect of the invention to provide a combination sulphur compound adsorbent and hydrogenation catalyst in a stabilization medium which reduces the time necessary for hydrogenation of edible oils from that of conventional hydrogenation catalysts.
It is a further aspect of this invention to provide a method for improving the performance of hydrogenation catalysts used in edible oil hydrogenation, where the edible oil is contaminated with sulphur-based compounds.
Still further objects and advantages will become apparent from consideration of the ensuing description of a preferred embodiment of the invention and examples thereof.
In accordance with the present invention there is provided a combination oil hydrogenation catalyst/sulphur adsorbent comprising
a) an oil hydrogenation catalyst and
b) a zeolite sulphur adsorbent.
Preferably, the oil hydrogenation catalyst and zeolite sulphur adsorbent are blended with a stabilization medium in which the catalyst and the adsorbent are admixed. Preferably the oil hydrogenation catalyst is a nickel on refractory oxide catalyst. The zeolite sulphur adsorbent is preferably a low silica faujasite with a silica to alumina ratio from about 1.8:1 to about 2.1:1, wherein the cations on the low silica faujasite are ion exchanged in an inequivalent excess of equilibrium of zinc ions or zinc containing cations or polycations.
The stabilization medium is any encapsulation medium which can encapsulate the oil hydrogenation catalyst and the zeolite sulphur adsorbent, and preferably is a saturated triglyceride with a low iodine value. The mixture of the hydrogenation catalyst and the sulphur adsorbing zeolite may also be stabilized by using an air/carbon dioxide mixture which produces a deactivation reaction of the reduced active metal species, as opposed to encapsulation with the stabilization medium.
The invention is also a process for the production of a combination oil hydrogenation catalyst and sulphur adsorbent stabilized in a stabilization medium comprising preparing the oil hydrogenation catalyst, acquiring the zeolite sulphur adsorbent, preparing the stabilization medium, and mixing the catalyst and adsorbent with the stabilization medium. Alternatively, the catalyst/zeolite mixture can be stabilized using an air/carbon dioxide blend to form a combination product.
The invention is also a process for hydrogenation of sulphur-contaminated vegetable, animal, marine, or mineral oils, and removal of sulphur-compound contamination from those oils during hydrogenation comprising:
a) preparing a combination product comprising an oil hydrogenation catalyst and sulphur adsorbent, blended with a stabilization medium,
b) mixing that combination product with an edible oil contaminated with sulphur compounds,
c) adsorbing a portion of the sulphur-contaminated compounds contained in the edible oil using the sulphur adsorbent, and
d) hydrogenating the oil using the hydrogenation catalyst.